Organic lighting emitting diode display device and method of fabricating the same

ABSTRACT

An organic lighting emitting diode display device (OLED display device) and a method of fabricating the same. The OLED display device includes: a substrate; a first electrode disposed on the substrate; an emission layer disposed on the first electrode; a second electrode disposed on the emission layer; and a hole injection layer disposed between the first electrode and the emission layer or between the emission layer and the second electrode, and formed of an inorganic semiconductor material, which evaporates at a temperature of 1100° C. or less. The method includes forming the hole injection layer between the first electrode and the second electrode, by thermally evaporating the inorganic semiconductor material, at a temperature of 1100° C., or less.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Application No.2006-129627, filed Dec. 18, 2006, in the Korean Intellectual PropertyOffice, the disclosure of which is hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to an organic lighting emittingdiode display device (OLED display device) and a method of fabricatingthe same, and more particularly, to an OLED display device including ahole injection layer, formed by thermal evaporation using an inorganicsemiconductor material, which can be thermally evaporated, and a methodof fabricating the same.

2. Description of the Related Art

An OLED display device comprises a substrate, an anode disposed on thesubstrate, an emission layer disposed on the anode, and a cathodedispose on the emission layer. In such an OLED display device, when avoltage is applied between the anode and the cathode, a hole (positivelycharged particle) and an electron are injected into the emission layer,and then recombined to create an exciton, which transitions from anexcited state to a ground state, to thereby emit light.

The OLED display device may comprise at least one selected from thegroup consisting of a hole injection layer, a hole transport layer, anelectron transport layer, and an electron injection layer. The holeinjection layer can be disposed between the anode and the emission layerto effectively inject the hole from the anode into the emission layer.In a conventional OLED display device, these layers are organic thinfilms formed of an organic material. However, especially, the holeinjection layer formed of an organic material has some problems, forexample, poor interface characteristics with an anode formed of atransparent conductive material, such as, indium tin oxide (ITO) orindium zinc oxide (IZO), and damage occurring when the anode is formedby sputtering. Moreover, the hole injection layer cannot completelyprotect the underlying emission layer from the damage.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an organic lighting emittingdiode display device (OLED display device), in which interfacecharacteristics between an anode and a hole injection layer areimproved. The display device is driven with a lower driving voltage, andhas an improved life span. Aspects of the present invention relate to amethod of fabricating the display device.

According to an aspect of the present invention, an OLED display devicecomprises: a substrate; a first electrode disposed on the substrate; anemission layer disposed on the first electrode; a second electrodedisposed on the emission layer; and a hole injection layer disposedbetween the first electrode and the emission layer, or between theemission layer and the second electrode. The hole injection layer isformed of an inorganic semiconductor material, which evaporates at atemperature of 1100° C., or less.

According to another aspect of the present invention, a method offabricating an OLED comprises: preparing a substrate; forming a firstelectrode on the substrate; forming an emission layer on the firstelectrode; forming a second electrode on the emission layer; and forminga hole injection layer of an inorganic semiconductor material, whichevaporates at a temperature of 1100° C. or less, between the firstelectrode and the emission layer, or between the emission layer and thesecond electrode.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent, and more readily appreciated, from the following descriptionof the embodiments, taken in conjunction with the accompanying drawingsof which:

FIG. 1 is a cross-sectional view of an organic lighting emitting diodedisplay device (OLED display device) including a hole injection layer,according to an exemplary embodiment of the present invention;

FIG. 2 is a graph illustrating the relationship between driving voltageand current density in an Example and a Comparative Example; and

FIG. 3 is a graph illustrating the relationship between the life spanand the emission rate in the Example and the Comparative Example.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The exemplary embodiments are described below, in order toexplain the present invention, by referring to the figures. As referredto herein, when a first element is said to be “disposed” on a secondelement, the first element can directly contact the second element, orone or more other elements can be located therebetween.

FIG. 1 is a cross-sectional view of an organic lighting emitting diodedisplay device (OLED display device) 200, according to an exemplaryembodiment of the present invention. Referring to FIG. 1, a firstelectrode 110 is formed on a substrate 100. The substrate can be formedof, for example, glass, stainless steel, plastic, or the like. Thesubstrate 100 may include at least one thin film transistor (notillustrated), which is in contact with the first electrode 110.

The first electrode 110 may be formed of magnesium (Mg), calcium (Ca),aluminum (Al), silver (Ag), barium (Ba), or an alloy thereof. The firstelectrode 110 may be a transparent or reflective electrode. Thetransparent electrode is thinly formed to permit light transmissionthere through, while the reflective electrode is thickly formed toreflect light. The first electrode 110 may act as a cathode. The firstelectrode 110 may be formed by, for example, sputtering, vapor phasedeposition, ion beam deposition, electron beam deposition, or laserablation.

The OLED display device 200 can include an electron injection layer 120,an electron transport layer 130, and/or a hole blocking layer 140,disposed on the first electrode 110. The electron injection layer 120serves to facilitate electron injection into an emission layer. Theelectron injection layer 120 may be formed of, for example,tris(8-quinolinolate)aluminum (Alq3), lithium fluoride (LiF), a gallium(Ga) complex, or 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(PBD). The electron transport layer 130 serves to facilitate electrontransport into the emission layer 150. The electron transport layer 130may be formed of a polymer such as PBD,3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenyl)-1,2,4-triazole (TAZ) orspiro-PBD, or a low molecular weight material, such as, Alq3, BAlq orSAlq. The hole blocking layer 140 may be omitted when the emission layeris a fluorescent emission layer. The hole blocking layer 140 serves toprevent the diffusion of excitons generated from the emission layer,when driving an OLED. The hole blocking layer 140 may be formed of, forexample, bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenyl)-aluminum(BAlq), bathocuproin (BCP), CF-X, TAZ, or spiro-TAZ. The electroninjection layer 120, the electron transport layer 130, or the holeblocking layer 140 may be formed by, for example, deposition, spincoating, inkjet printing, or laser induced thermal imaging.

The emission layer 150 is disposed on the hole blocking layer 140. Theemission layer 150 may be a phosphorescent or fluorescent emissionlayer. When the emission layer 150 is a fluorescent emission layer, theemission layer 150 may include one selected from the group consisting ofdistyrylarylene (DSA), a distyrylaryiene derivative, distyrylbenzene(DSB), a distyrylbenzene derivative,4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi), a DPVBi derivative,spiro-DPVBi, and spiro-sixphenyl (spiro-6P). The emission layer 150 mayinclude a dopant material selected from the group consisting ofstyrylamine-based, perylene-based, and distyrylbiphenyl-based materials.

Alternatively, when the emission layer 150 is a phosphorescent emissionlayer, the emission layer 150 may include one selected from the groupconsisting of an arylamine-based, an carbazole-based and a spiro-basedmaterial, as a host material. The host material can include one selectedfrom the group consisting of 4,4-N,N-dicarbazole-biphenyl (CBP), a CBPderivative, N,N-dicarbazolyl-3,5-benzene (mCP), an mCP derivative, and aspiro derivative. The emission layer 150 may include, as a dopant, aphosphorescent organic metal complex having one central metal selectedfrom the group consisting of iridium (Ir), platinum (Pt), terbium (Tb),and europium (Eu). In addition, the phosphorescent organic metal complexmay be one selected from the group consisting of PQIr, PQIr(acac),PQ2Ir(acac), PIQIr(acac), and PtOEP.

If the OLED display device 200 is a full color device, the emissionlayer 150 may be formed by deposition, inkjet printing, or laser inducedthermal imaging.

The OLED display device 200 can include an electron blocking layer 160and a hole transport layer 170, disposed on the emission layer 150. Theelectron blocking layer 160 serves to prevent the diffusion of excitons,generated from the emission layer 150 while driving the OLED displaydevice 200. The electron blocking layer 160 may be formed of BAlq, BCP,CF-X, TAZ, or spiro-TAZ, for example. The hole transport layer 170serves to facilitate hole transport to the emission layer 150, and maybe formed of a low molecular weight material, such as,N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)benzidine (α-NPB),N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine (TPD), s-TAD and4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine (MTDATA),or a polymer, such as PVK. Meanwhile, the electron blocking layer 160and/or the hole transport layer 170, may be formed by deposition, spincoating, inkjet printing, or laser induced thermal imaging, for example.

The OLED display device 200 can include a hole injection layer 180disposed on the hole transport layer 170. The hole injection layer 180can be formed of an inorganic semiconductor material, which canevaporate at a temperature of 1100° C., or less. The inorganicsemiconductor material is an inorganic material with semiconductorproperties. The OLED display device 200 can include a second electrode190 as a hole injection electrode, disposed on the hole injection layer180. The second electrode 190 can be formed of a transparent electrodematerial, such as, indium tin oxide (ITO), indium zinc oxide (IZO), orzinc oxide (ZnO). The hole injection layer 180, formed of the inorganicsemiconductor material, and the second electrode 190, formed of thetransparent electrode material, which is an inorganic material, may havebetter interface characteristics than when a hole injection layer formedof an organic material is used. Also, compared to a surface of the holeinjection layer formed by depositing an organic material, the inorganicsemiconductor material has better morphology characteristics. Thus, theimprovement of the interface characteristics between the hole injectionlayer 180 and the second electrode 190, results in a lower drivingvoltage when driving the OELD display device 200, and a longer lifespan.

The hole injection layer 180 is formed by the thermal evaporation of aninorganic semiconductor material that evaporates at a temperature of1100° C., or less. Exemplary thermal evaporation equipment includes aboat or furnace to contain a deposition material, and a hot wire to heatthe boat or furnace. The hot wire is durable at 1100° C., or less.Therefore, when the hole injection layer 180 is formed by thermalevaporation, the inorganic semiconductor material evaporates at 1100°C., or less. The inorganic semiconductor material may be, for example,vanadium pentoxide (V₂O₅), tungsten oxide (WO₃), molybdenum oxide(MoO₃), or boron oxide (B₂O₃). This process can prevent damage toorganic layers, occurring during the formation of a hole injectionlayer, using sputtering. The process does not need special sputteringequipment, because the process may be performed by the equipment used todeposit the organic layer. Moreover, as compared to a hole injectionlayer formed by sputtering an inorganic semiconductor material, the holeinjection layer 180, formed of the inorganic semiconductor materialusing the thermal evaporation, may have an improved density andmorphology characteristics. As a result, in an inverted structure havingan upper anode formed of ITO, IZO, or ZnO disposed on the hole injectionlayer 180 using sputtering, the damage by sputtering to the organiclayer, including the underlying emission layer 150, may be minimized.

In the thermal evaporation, the inorganic semiconductor material may beevaporated from a boat or furnace in a thermal evaporation apparatus, byapplying current to the boat or furnace, or by using a furnace for ahigh temperature cell. Also, the thermal evaporation may be performed ina vacuum, or a nitrogen atmosphere.

The hole injection layer 180 is formed to a thickness of from 5 to 1000Å. Within this thickness range, the underlying organic layer can beprotected from damage during the formation of a second electrode bysputtering. An overall thickness of the OLED display device 200 isthereby not excessively thick, which may be more effective when drivingthe device 200.

The OLED display device 200 includes second electrode 190 disposed onthe hole injection layer 180. The second electrode 190 may be atransparent or reflective electrode. The transparent electrode may beformed of ITO, IZO, or ZnO. The reflective electrode may be formed in astacked structure, in which a reflective layer is disposed on atransparent electrode material. The reflective layer may be formed ofAg, Al, chromium (Cr), Mo, W, titanium (Ti), tantalum (Ta), or an alloythereof for example. In this case, the transparent electrode materialmay be ITO, IZO, or ZnO, for example. Thus, the second electrode 190(anode) may be completed.

Aspects of the present invention will now be explained, with referenceto the following examples, but the scope of the present invention willnot be limited thereto.

EXAMPLE

A cathode was formed by depositing Al, having a thickness of 2000 Å, ona substrate. An electron injection layer was formed by depositing LiF,having a thickness of 5 Å, on the cathode. An electron transport layerwas formed by depositing Alq3, having a thickness of 200 Å, on theelectron injection layer. TMM004 (available from Merck) was doped with 2wt % GD33 (available from UDC) and deposited to a thickness of 300 Å onthe electron transport layer, thereby forming an emission layer. A holetransport layer was formed by depositing IDE320 (available fromIdemitsu) to a thickness of 150 Å, on the emission layer. A holeinjection layer was formed by thermally evaporating WO3, having athickness of 500 Å, on the hole transport layer, in a vacuum. Finally,an anode was formed by depositing ITO, having a thickness of 1000 Å, onthe hole injection layer, by sputtering.

The life span of the OLED display device was measured at a brightness of5000 nit and the current density according to driving voltage of theOLED display device.

COMPARATIVE EXAMPLE

A cathode was formed by depositing Al having a thickness of 2000 Å on asubstrate. An electron injection layer was formed by depositing LiFhaving a thickness of 5 Å on the cathode. An electron transport layerwas formed by depositing Alq3 having a thickness of 200 Å on theelectron injection layer. TMM004 (available from Merck) was doped with 2wt % GD33 (available from UDC) to be deposited to a thickness of 300□ onthe electron transport layer, thereby forming an emission layer. A holetransport layer was formed by depositing IDE320 (available fromIdemitsu) to a thickness of 150 Å on the emission layer. A holeinjection layer was formed by thermally evaporating IDE406 (availablefrom Idemitsu) to a thickness of 500 Å on the hole transport layer in avacuum. Finally, an anode was formed by depositing ITO to a thickness of1000 Å on the hole injection layer by sputtering.

The life span of the OLED display device was measured at a brightness of5000 nit, and a current density according to driving voltage of the OLEDdisplay device. FIG. 2 is a graph illustrating the relationship betweendriving voltage and current density in an Example and a ComparativeExample. The x axis represents driving voltage (V), and the y axisrepresents current density (mA/cm2).

Referring to FIG. 2, in the Example, when the driving voltages are 6, 7,and 8V, the current densities were approximately 90, 180, and 320mA/cm2, respectively. However, in the Comparative Example, when thedriving voltages are 6, 7, and 8V the current densities were 80, 150,and 250 mA/cm2. It can be seen that the difference between the currentdensities, in the Example and the Comparative Example, increased withthe driving voltage. That is, as the driving voltage increased, thedevice in the Example had a higher current density than that in theComparative Example, thereby demonstrating improved driving voltagecharacteristics. As described above, the Example demonstrated improvedinterface characteristics with an anode, by forming a hole injectionlayer of an inorganic material that evaporated at 1100° C., or less, bythermal evaporation, and demonstrated improved driving voltagecharacteristics as compared to the Comparative Example, in which a holeinjection layer was formed of an organic material, by thermalevaporation.

FIG. 3 is a graph illustrating the relationship between a life span andan emission rate, at a brightness of 5000 nit, in the Example and theComparative Example. The x axis represents life span (h), and the y axisrepresents an emission rate (%). Referring to FIG. 3, when driven at abrightness of 5000 nit, in the Example, the emission rate was reduced by42% after being driven for 1500 hrs, however, in the Comparative Examplethe emission rate was reduced by 50% after the same driving period.Accordingly, the Example demonstrated improved interfacecharacteristics, by having a hole injection layer formed of an inorganicmaterial that was evaporated at 1100° C., or less, and thus, showed alonger life span than the Comparative Example, in which a hole injectionlayer was formed of an organic material.

According to aspects of the present invention as described above, a holeinjection layer is formed of an inorganic semiconductor materialevaporated at a temperature of 1100° C., or less, by thermalevaporation, thereby improving interface characteristics with an anode.Thus, a driving voltage thereof may be reduced, and the life spanthereof may be improved. Also, since the inorganic material can also bethermally evaporated using equipment for thermally evaporating anorganic material, separate equipment is not required.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An organic lighting emitting diode (OLED) display device, comprising:a substrate; a first electrode disposed on the substrate; an emissionlayer disposed on the first electrode; a second electrode disposed onthe emission layer; and a hole injection layer disposed between thefirst electrode and the second electrode, comprising an inorganicsemiconductor material that evaporates at a temperature of 1100° C. orless.
 2. The OLED display device according to claim 1, wherein theinorganic semiconductor material is selected from the group consistingof V₂O₅, WO₃, MoO₃ and B₂O₃.
 3. The OLED display device according toclaim 1, wherein the first electrode is a cathode and the secondelectrode is an anode.
 4. The OLED display device according to claim 3,wherein the anode comprises indium tin oxide (ITO), indium zinc oxide(IZO), or zinc oxide (ZnO).
 5. The OLED display device according toclaim 1, wherein the hole injection layer has a thickness of from 5 to1000 Å.
 6. The OLED display device according to claim 1, furthercomprising at least one selected from the group consisting of a holetransport layer, a hole blocking layer, an electron blocking layer, anelectron transport layer, and an electron injection layer, disposedbetween the first and second electrodes.
 7. A method of fabricating anorganic lighting emitting diode (OLED) display device, comprising:forming a first electrode on a substrate; forming an emission layer onthe first electrode; forming a second electrode on the emission layer;and forming a hole injection layer of an inorganic semiconductormaterial that evaporates at a temperature of 1100° C. or less, betweenthe first electrode and the second electrode.
 8. The method according toclaim 7, wherein the inorganic semiconductor material is selected fromthe group consisting of V₂O₅, WO₃, MoO₃, and B₂O₃.
 9. The methodaccording to claim 8, wherein the hole injection layer is formed bythermal evaporation.
 10. The method according to claim 9, wherein thethermal evaporation is performed in a vacuum atmosphere.
 11. The methodaccording to claim 9, wherein the thermal evaporation is performed in anitrogen atmosphere.
 12. The method according to claim 7, wherein thesecond electrode is formed by sputtering.
 13. The method according toclaim 7, wherein the emission layer is formed by deposition.
 14. TheOLED display device according to claim 3, wherein the hole injectionlayer is disposed between the emission layer and the anode.
 15. The OLEDdisplay device according to claim 1, wherein the first electrodecomprises a reflective material selected from the group consisting ofmagnesium (Mg), calcium (Ca), aluminum (Al), silver (Ag), barium (Ba),and an alloy thereof.
 16. The OLED display device according to claim 1,wherein the emission layer is a material selected from the groupconsisting of distyrylarylene (DSA), a distyrylaryiene derivative,distyrylbenzene (DSB), a distyrylbenzene derivative,4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi), a DPVBi derivative,spiro-DPVBi, and spiro-sixphenyl (spiro-6P).
 17. The OLED display deviceaccording to claim 1, wherein the emission layer comprises a dopantmaterial selected from the group consisting of styrylamine-based,perylene-based, and distyrylbiphenyl-based materials.
 18. An organiclighting emitting (OLED) diode display device, comprising. a cathode; anemission layer disposed on the cathode; a hole injection layer disposedon the emission layer, comprising an inorganic semiconductor materialselected from the group consisting of V₂O₅, WO₃, MoO₃ and B₂O₃; and ananode disposed on the hole injection layer.
 19. The OLED display deviceaccording to claim 18, further comprising a substrate disposed on thecathode.
 20. The OLED display device according to claim 18, furthercomprising at least one selected from the group consisting of a holetransport layer, a hole blocking layer, an electron blocking layer, anelectron transport layer, and an electron injection layer, disposedbetween the anode and the cathode.